powerpc/fadump: use FADump instead of fadump for how it is pronounced

to minimize the total elapsed time until the system is back

in production use.

- Firmware assisted dump (fadump) infrastructure is intended to replace

- Firmware-Assisted Dump (FADump) infrastructure is intended to replace

  the existing phyp assisted dump.

- Fadump uses the same firmware interfaces and memory reservation model

  as phyp assisted dump.

- Unlike phyp dump, fadump exports the memory dump through /proc/vmcore

- Unlike phyp dump, FADump exports the memory dump through /proc/vmcore

  in the ELF format in the same way as kdump. This helps us reuse the

  kdump infrastructure for dump capture and filtering.

- Unlike phyp dump, userspace tool does not need to refer any sysfs

  interface while reading /proc/vmcore.

- Unlike phyp dump, fadump allows user to release all the memory reserved

- Unlike phyp dump, FADump allows user to release all the memory reserved

  for dump, with a single operation of echo 1 > /sys/kernel/fadump_release_mem.

- Once enabled through kernel boot parameter, fadump can be

- Once enabled through kernel boot parameter, FADump can be

  started/stopped through /sys/kernel/fadump_registered interface (see

  sysfs files section below) and can be easily integrated with kdump

  service start/stop init scripts.

   in a clean, consistent state.

-  Once the dump is copied out, the memory that held the dump

   is immediately available to the running kernel. And therefore,

   unlike kdump, fadump doesn't need a 2nd reboot to get back

   unlike kdump, FADump doesn't need a 2nd reboot to get back

   the system to the production configuration.

The above can only be accomplished by coordination with,

         boot successfully. For syntax of crashkernel= parameter,

         refer to Documentation/admin-guide/kdump/kdump.rst. If any offset is

         provided in crashkernel= parameter, it will be ignored

         as fadump uses a predefined offset to reserve memory

         as FADump uses a predefined offset to reserve memory

         for boot memory dump preservation in case of a crash.

-  After the low memory (boot memory) area has been saved, the

Hence, the implementation uses the Linux kernel's Contiguous Memory

Allocator (CMA) for memory reservation if CMA is configured for kernel.

With CMA reservation this memory will be available for applications to

use it, while kernel is prevented from using it. With this fadump will

use it, while kernel is prevented from using it. With this FADump will

still be able to capture all of the kernel memory and most of the user

space memory except the user pages that were present in CMA region::

The tools to examine the dump will be same as the ones

used for kdump.

How to enable firmware-assisted dump (fadump):

How to enable firmware-assisted dump (FADump):

----------------------------------------------

1. Set config option CONFIG_FA_DUMP=y and build kernel.

2. Boot into linux kernel with 'fadump=on' kernel cmdline option.

   By default, fadump reserved memory will be initialized as CMA area.

   By default, FADump reserved memory will be initialized as CMA area.

   Alternatively, user can boot linux kernel with 'fadump=nocma' to

   prevent fadump to use CMA.

   prevent FADump to use CMA.

3. Optionally, user can also set 'crashkernel=' kernel cmdline

   to specify size of the memory to reserve for boot memory dump

   preservation.

Here is the list of files under kernel sysfs:

 /sys/kernel/fadump_enabled

    This is used to display the fadump status.

    This is used to display the FADump status.

    - 0 = fadump is disabled

    - 1 = fadump is enabled

    - 0 = FADump is disabled

    - 1 = FADump is enabled

    This interface can be used by kdump init scripts to identify if

    fadump is enabled in the kernel and act accordingly.

    FADump is enabled in the kernel and act accordingly.

 /sys/kernel/fadump_registered

    This is used to display the fadump registration status as well

    as to control (start/stop) the fadump registration.

    This is used to display the FADump registration status as well

    as to control (start/stop) the FADump registration.

    - 0 = fadump is not registered.

    - 1 = fadump is registered and ready to handle system crash.

    - 0 = FADump is not registered.

    - 1 = FADump is registered and ready to handle system crash.

    To register fadump echo 1 > /sys/kernel/fadump_registered and

    To register FADump echo 1 > /sys/kernel/fadump_registered and

    echo 0 > /sys/kernel/fadump_registered for un-register and stop the

    fadump. Once the fadump is un-registered, the system crash will not

    FADump. Once the FADump is un-registered, the system crash will not

    be handled and vmcore will not be captured. This interface can be

    easily integrated with kdump service start/stop.

 /sys/kernel/fadump_release_mem

    This file is available only when fadump is active during

    This file is available only when FADump is active during

    second kernel. This is used to release the reserved memory

    region that are held for saving crash dump. To release the

    reserved memory echo 1 to it::

(Assuming debugfs is mounted on /sys/kernel/debug directory.)

 /sys/kernel/debug/powerpc/fadump_region

    This file shows the reserved memory regions if fadump is

    This file shows the reserved memory regions if FADump is

    enabled otherwise this file is empty. The output format

    is::

      <region>: [<start>-<end>] <reserved-size> bytes, Dumped: <dump-size>

    and for kernel DUMP region is:

    DUMP: Src: <src-addr>, Dest: <dest-addr>, Size: <size>, Dumped: # bytes

    e.g.

    Contents when fadump is registered during first kernel::

    Contents when FADump is registered during first kernel::

      # cat /sys/kernel/debug/powerpc/fadump_region

      CPU : [0x0000006ffb0000-0x0000006fff001f] 0x40020 bytes, Dumped: 0x0

      HPTE: [0x0000006fff0020-0x0000006fff101f] 0x1000 bytes, Dumped: 0x0

      DUMP: [0x0000006fff1020-0x0000007fff101f] 0x10000000 bytes, Dumped: 0x0

    Contents when fadump is active during second kernel::

    Contents when FADump is active during second kernel::

      # cat /sys/kernel/debug/powerpc/fadump_region

      CPU : [0x0000006ffb0000-0x0000006fff001f] 0x40020 bytes, Dumped: 0x40020

      DUMP: [0x0000006fff1020-0x0000007fff101f] 0x10000000 bytes, Dumped: 0x10000000

          : [0x00000010000000-0x0000006ffaffff] 0x5ffb0000 bytes, Dumped: 0x5ffb0000

NOTE:

      Please refer to Documentation/filesystems/debugfs.txt on

      how to mount the debugfs filesystem.

 - Need to come up with the better approach to find out more

   accurate boot memory size that is required for a kernel to

   boot successfully when booted with restricted memory.

 - The fadump implementation introduces a fadump crash info structure

 - The FADump implementation introduces a FADump crash info structure

   in the scratch area before the ELF core header. The idea of introducing

   this structure is to pass some important crash info data to the second

   kernel which will help second kernel to populate ELF core header with